At least one of the embodiments of the present invention generally relates to improvements in a medical x-ray imaging system, and more particularly relates to an improved interface between a positioning arm and an x-ray tube.
X-ray imaging systems typically include an x-ray tube, a detector, and a positioning arm, such as a C-arm, supporting the x-ray tube and the detector. In operation, an imaging table, on which a patient is positioned, is located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as X-rays, toward the patient. The radiation typically passes through the patient positioned on the imaging table and impinges on the detector. As the radiation passes through the patient, anatomical structures inside the patient cause spatial variances in the radiation received at the detector. The detector then translates the radiation variances into an image which may be employed for clinical evaluations.
Typically, the x-ray tube is directly mounted to the positioning arm. The x-ray tube is rigidly fastened to the positioning arm through fasteners such as bolts, screws, and the like. Typically, the x-ray tube and the positioning arm directly contact each other through their respective mounting surfaces. Additionally, the x-ray tube and the positioning arm contact each other through the fasteners. That is, one portion of each fastener, such as a head of a bolt, directly contacts the x-ray tube, while the other portion, such as a nut, directly contacts the positioning arm. Washers may be positioned between the mounting surfaces and the fastener. The direct contact between the x-ray tube and positioning arm, and the additional contact from the fasteners typically provide an unimpeded vibrational path between the x-ray tube and the positioning arm.
The x-ray tube typically vibrates during use. The vibrations caused by the x-ray tube may be translated from the x-ray tube to the positioning arm. The subsequent vibration of the positioning arm typically causes acoustic noise. The acoustic noise generated from the vibration of the positioning arm due to the vibration of the x-ray tube may exceed the ambient background noise. The excessive noise generated during x-ray imaging may be unsettling to patients and irritating to physicians and x-ray technicians.
X-rays are produced when high-speed electrons are suddenly decelerated, for example, when a metal target, is struck by electrons that have been accelerated through a potential difference of several thousand volts. Typically, x-ray emitters include an anode and a cathode. In order to manage the resulting heat on the target from the cathode during the x-ray emission process, the anode is rotated at a high rate of speed. Typically, the anode is connected to an axle. The axle is in turn retained by a bearing. The bearing rotates the axle. The bearing is rotated by a motor. Therefore, the rotation of the bearing causes the anode to rotate.
The rotation of the bearing typically causes the x-ray tube to vibrate. That is, the vibrations produced by the bearing are transmitted from the emitter to the x-ray tube casing. The vibrations are then transmitted into the positioning arm, or C-arm through the direct contact of the mounting surfaces of the x-ray tube and the positioning arm. Additionally, the vibrations are also transmitted from the x-ray tube to the fastener. The vibrations are then transmitted from the fastener to the positioning arm. The vibrations translated to the positioning arm produce acoustic noise, or acoustic energy.
The direct-contact interface between the x-ray tube and the positioning arm provides a path along which the vibrations travel. Because the x-ray tube and the positioning arm are securely fastened to one another, the impedance for the transmission of the vibration is matched. The matched impedance provides the vibration an unimpeded path from the x-ray tube to the positioning arm.
In order to diminish the noise produced within x-ray systems, some systems include an expensive fluid film bearing, or spiral groove bearing. The spiral groove bearing uses a liquid metal, such as Gallium, to reduce the vibrations caused by the bearing. Vibration energy in the expensive spiral groove bearing is small due to the fluid film lubrication in the bearing.
Thus a need has existed to reduce the amount of noise produced within x-ray systems. Further a need has existed for an interface that efficiently and inexpensively reduces the amount of noise produced within an x-ray system.
In accordance with an embodiment of the present invention, an x-ray system has been developed that substantially reduces the amount of acoustic noise produced within the system. The x-ray system includes a positioning arm, such as a C-arm, an x-ray tube, an x-ray detector; and an acoustic dampening interface, or isolation layer. The acoustic dampening interface may be a rubber isolator that mounts between the x-ray tube and a first end, or prong, of the positioning arm. The detector mounts on a second end, or prong, of the positioning arm. The isolator substantially absorbs acoustic energy, in the form of vibrations, generated by the x-ray tube. That is, the isolator causes a vibrational impedance mismatch between the x-ray tube and the positioning arm, or C-arm, when vibrational energy is transmitted from an emitter within the x-ray tube to the rubber isolator.
The x-ray tube includes a vibrational insulation layer. The vibrational insulation includes foam layers separated by a lead barrier layer. The foam layers may be made of polyester foam or urethane foam. In one embodiment of the present invention, the lead barrier layer has a density of one pound per square foot.
The rubber isolator of one embodiment of the present invention includes a rubber isolation tube. The rubber isolation tube extends through a hole formed within a mounting plate of the x-ray tube. The rubber isolation tube clamps onto the tube mounting plate. The rubber isolation tube also includes a steel inner sleeve. The inner sleeve retains a fastener, such as a screw, bolt and the like. The rubber isolation tube isolates, or separates the x-ray tube from direct contact with the fastener.
The rubber isolator of another embodiment of the present invention includes a rubber washer and a rubber isolation ring. The rubber washer isolates, or separates the x-ray tube from direct contact with a fastener. Further, the rubber isolation ring separates the x-ray tube from the positioning arm. In another embodiment, a rubber isolation layer substantially occupies the space between the x-ray tube and the positioning arm.
In another embodiment of the present invention, the noise reduction system may be implemented in a computerized tomography (CT) imaging system. The CT system may include a gantry, a CT tube, and a rubber isolator mounted between the gantry and the CT tube.